This study aimed to evaluate the effect of surgical and immunocastration of post-pubertal beef cattle on their sexual and aggressive behaviour, growth and meat quality. Forty mixed-breed bulls were assigned to one of four treatments (n = 10): steers (S) castrated at 11 months of age, late castrates (LC) surgically castrated at 17 months of age (Day 1), immunocastrates (I) vaccinated against GnRH at 17 months of age (Day 1) and entire bulls (B). Sexual and aggressive behaviour was monitored at monthly intervals and prior to slaughter, animals were weighed and blood sampled fortnightly. All treatments were slaughtered at 22 months of age after which carcass composition and meat quality (pHu) were assessed. Plasma testosterone concentrations declined to the level of steers by Day 14 for late castrates and by Day 28 for immunocastrates and remained lower than for entire bulls through to slaughter. Entire bulls had a heavier hot carcass weight (HCW) than I, LC and S. Immunocastrates were heavier than LC and S. Treatment had no effect on pHu although late castrates tended to have a higher mean pHu than immunocastrates and steers. From Day 0 to slaughter, rates of sexual and aggressive behaviour declined significantly for bulls, late castrates and immunocastrates to be similar to steers. There was a tendency for bulls to show higher levels of both sexual and aggressive behaviour during lairage.
Proceedings of the New Zealand Society of Animal Production, Volume 56, , 394-397, 1996
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